LeetCode OJ：Happy Number（欢乐数）

Write an algorithm to determine if a number is "happy".

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 19 is a happy number

• 12 + 92 = 82
• 82 + 22 = 68
• 62 + 82 = 100
• 12 + 02 + 02 = 1

欢乐数，就是不断将位的平方相加为新数，看看最后得到的数是不是1，是的话就是欢乐数，否则不是。代码比较简单，用一个set保存下来已经求到过的不是1的数字，一旦

后期某个计算到的数字能在set中找到（不是1），那么就一定进入到死循环当中了。这是就应该返回false， 否则一旦某个计算结果是1那么久返回true，代码见下：

 1 class Solution {
 2 public:
 3     bool isHappy(int n) {
 4         set<int> sample;
 5         sample.insert(n);
 6         int s = 0;
 7         for(;;){
 8             while(n != 0){
 9                 s += (n % 10) * (n % 10);
10                 n /= 10;
11             }
12             if(s == 1)
13                 return true;
14             else{
15                 if(sample.find(s) != sample.end())
16                     return false;
17                 sample.insert(s);
18                 n = s;
19                 s = 0;
20             }
21         }
22     }
23 };